1. Field of the Invention
The present invention relates to electrical matching networks, and more particularly to a broadband matching network for use with a Helmholtz acoustic resonator in deep water.
2. Description of the Prior Art
As acousticians become increasingly more interested in the lower regions of the acoustic frequency domain, concern has increased over the modeling of the ocean floor and its accompanying sublayers as transmission media that refract, diffract, diffuse and dissipate as well as reflect sound waves that eventually reach a receiving hydrophone in the water column. Geoacoustic and geophysical models of ocean floor acoustic interaction which take all energy paths into account are needed as inputs to acoustic propagation loss calculations. Thus, the development of instrumentation and field measurements systems capable of acquiring the necessary types of geophysical, geoacoustic data with sufficient accuracy, resolution and frequency response is critical.
The technology as developed by the petroleum industry allows the collection on a continuous basis of high resolution layered structure, interface reflectivity as a function of grazing angle, velocity and attenuation as a function of depth, migration of side reflections to true position, and direct interpretation of lithology and saturating pore fluid. Presently these data are collected using surface sources and receivers, but the measurement geometries are such that this is possible only in shallow water. However, if a near-bottom source and receiver array is used, the geometries are identical to shallow-water techniques, and a wealth of proven processing technology becomes available. Specifically, if the outputs of a sequence of hydrophones spaced over a distance which is long in relation to receiver-bottom distance is individually recorded, along with an acoustic source keyed from the surface and in line with the hydrophones, and if such a device is towed near the sea floor in the deep ocean, such a geometry is achieved.
A Helmholtz resonator transducer is used as the acoustic source and has an operating bandwidth in the lower regions of the acoustic frequency domain. However, the output of the Helmholtz resonator transducer is asymmetrical in shape, reducing the acoustic usable bandwidth. What is desired is means for expanding the acoustic usable bandwidth with a concomitant reduction in input pulse power for a given output pulse power.